Human beings are made up of two distinct parts; the physical body and the non-physical mind.
Idealists believe that only the mind exists and everything that we perceive in the physical world is merely a composition.
Mental states are intrisically knowable, but physical states require inference and experience.
In reducing all experiences to physical processes, we are unable to explain the full depth of "experience" and what it feels like. How can we reduce emotive activities like listening to music, watching a moving play, or seeing a beautiful piece to art to physical processes?
Frank Jackson put forward a version of the following argument in his article 'Epiphenomal Qualia' in 1982. Imagine an incredibly gifted scientist that was born deaf. He or she dedicates his life profession to studying hearing, and the processes and mechanisms involved in hearing sound. Finally, after knowing everything there is to know about hearing from a purely functional and physical perspective, the scientist undergoes an operation to repair his or her deafness. The knowledge argument proposes that this scientist, when they hear sound for the first time, will learn something new. The scientist will experience what it is like to hear. We call this qualitative way of experiencing something qualia . Not every experience can be reduced to something physical. The actual feeling of what it is to experience music and sound cannot be reduced to physical processes. Therefore, there must be a non-physical component to our experiences.
Evolutionary Argument Critics of dualism have often pointed to evolution as scientific evidence against the theory. As humans, we evolved from a single-cell organism, into the complex human species we have today. Because we began as a purely physical entity, it is impossible that a non-physical entity was later added. Our species evolved through random cellular mutations and the natural selection process. There is simply no scope for the evolution or development of the mind as a non-physical aspect of our species.
Not everything can be reduced to physical processes. Therefore, there must be a non-physical aspect of being human.
Humans evolved from single cells. Single cells do not have non-physical minds. Therefore, humans do not have non-physical minds.
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